Some people are replacing incandescent light bulbs with LED bulbs. The LED bulbs are direct replacements for incandescent lights, so a user simply unscrews an incandescent bulb from a socket and replaces it with an LED bulb. Many incandescent bulbs are operated by the use of a dimmer that controls the intensity of light emitted by an incandescent bulb. Most dimmers work by clipping the AC line voltage supplied to the incandescent bulb by the use of a triac. For example, the dimmer clips the positive and negative portions of the AC sinusoidal wave that is supplying power to the incandescent bulb. Because of the construction and inherent operating principles of the triac, the positive and negative portions of the AC voltage that are clipped by the triac are not equal.
The intensity of light emitted by an incandescent and an LED bulb is proportional to the current driving the bulb. Therefore, when the positive and negative portions of the sinusoidal wave driving the bulbs is clipped differently, the driving current will have a ripple. Incandescent lights have a very long time constant, meaning that they will glow for a period after power is removed. Therefore, a user is not likely to notice the inherent ripple of a dimmed incandescent light bulb. However, LEDs emit light based on current flow through a P-N junction and therefore do not glow or have a very short period in which they glow. As a consequence, the difference in conduction angles caused by the triac causes a noticeable and unpleasant flicker.